Field of the Invention
The present invention relates to flow regulators and, more particularly, automatic flow regulators for use during blood collection.
Description of Related Art
Needle assemblies are used for collecting specimens of fluid, such as blood, from a patient. Some such needle assemblies are intended for use with an evacuated tube and include a housing with a proximal end, a distal end, and a passage extending between the ends. Such needle assemblies further include at least one needle cannula mounted to the housing. The needle cannula includes a sharply pointed distal end that projects distally beyond the housing, a proximal end that projects proximally beyond the housing, and a lumen that provides communication between the opposed ends of the needle cannula. Some needle assemblies include separate proximal and distal cannulas and rely upon a portion of the housing to provide communication between the lumens of the respective cannulas. The distal end of the needle cannula typically is beveled to a tip that is sufficiently sharp for piercing the skin of the patient and accessing the vein or other source of fluid that is to be collected. The proximal end of the needle cannula is configured for piercing the rubber stopper on an evacuated tube. The proximal end of the needle cannula typically is covered by a needle pierceable resealable multi-sample sleeve. The sleeve is compressed by the rubber stopper of the evacuated tube and punctured by the proximal end of the needle cannula as the proximal end of the needle cannula is urged into communication with the evacuated tube. The evacuated tube is typically received by a needle holder secured to the proximal end of the housing.
The combined needle assembly and evacuated tube is employed by initially urging the pointed distal end of the needle cannula into a blood vessel of a patient. Once the targeted blood vessel has been accessed, the evacuated tube is urged into the needle holder such that the proximal point of the needle cannula pierces the septum of the tube. Low pressure conditions within the evacuated tube, as well as the patient's own vasculature pressure, generate a flow of blood from the patient through the needle cannula and into the evacuated tube. The evacuated tube may be removed from the needle holder after a sufficient quantity of blood has been collected. One or more additional evacuated tubes may similarly be urged into the open end of the needle holder for drawing one or more additional samples of blood to be analyzed. The needle cannula is then withdrawn from the patient after a sufficient volume of blood has been collected for the required analytical procedure.
During certain blood collection procedures, vein collapse of the patient occurs as a result of blood being removed too quickly from the patient's vein. Physiological conditions, such as elasticity of the vein wall, can contribute to this issue. With a conventional evacuated tube, there is a substantially instantaneous introduction of a vacuum pressure when the evacuated tube is attached to the non-patient end of the needle assembly or blood collection device. This strong vacuum pressure results in an initially high flow rate of blood out of the patient's vein. This abrupt outflow of blood coupled with the high elasticity of a patient's vein can lead to the vein wall being pulled down onto the cannula bevel and result in flow stoppage. Blood supply can also be a contributing factor of vein collapse. Most typical blood collection sites are in the patient's arm and hand. With these collection sites, the supply of blood available for collection resides below the collection side due to the one-way valves of the vein. In-flow of new blood to this area is limited as a result of the capillary blood vessels. In situations where there is limited resident blood, such as a hand collection site, the vacuum from the collection tube leads to a high flow rate out of the vein, which can lead to an outflow rate higher than the inflow rate of blood and a rapid depletion of the resident blood thereby leading to vein collapse.
With patients that are susceptible to vein collapse, syringes are commonly used for blood collection to provide the user with better control over the flow rate of blood out of the patient. However, the skill of the technician generally plays a large role in successfully using a syringe in a blood collection procedure. For instance, there can be a lot of variability in the amount of force the user exerts on the syringe plunger and the associated flow rates. Further, if not used appropriately, the syringe can achieve greater flow rates than a standard evacuated tube.